In magneto-optic recording systems, digital information is stored in a thin magnetic storage medium by locally magnetized regions or domains. The regions are magnetized to represent either ones or zeros. The information is written into the magnetic storage medium by raising the temperature of localized small regions of the magnetic medium to the Curie point temperature of the medium at the localized regions. This lowers the coercivity to a point which enables orientation of the magnetic domain in the medium by an external magnetic field. Stored information is read by Kerr or Faraday rotation of a polarized light beam incident upon the magnetic medium at the magnetized regions or domains. The shift in polarization is in the order of 1 degree and is employed to detect the ones and zeros. Systems for reading out these small rotational changes are well established in the optical storage industry. Optical recording and the design of conventional read/write heads is described in the book entitled "Optical Recording" authored by Alan B. Marchant, Addison-Wesley Publishing, 1990.
The size of the regions or domains determines the density of the digital information. The size of the localized regions is limited by diffraction of the light energy and is marginally improved by use of shorter wavelengths of light and higher numerical aperture lens.
In microscopy the diffraction limitation is overcome by employing near-field microscopy. In near-field microscopy the light beam is focused through a pinhole that is smaller than the diffraction limited spot size of the light beam. The pinhole is placed very close to the object. The size of the pinhole determines the definition of the microscope.
Betzig and others overcame the diffraction limitation in an optical recording system by employing near-field optics. They demonstrated areas of 20 nm diameter or better for the magnetized regions or domains. (E. Betzig, J. K. Trautman, R. Wolfe, P. L. Finn, M. H. Kryder and C. H. Chang, "Near-Field Magneto-Optics and Hi-Density Data Storage", Appl. Phys. Lett. 61, 142-144, (1992)).
In U.S. Pat. No. 5,125,750 there is disclosed an optical recording system including a read/write optical assembly for reading or writing from a magneto-optical medium. A solid immersion lens is interposed between the objective lens of the read/write head and the magnetic recording medium. The use of the solid immersion lens in conjunction with the objective lens decreases the spot size of the light focused on the recording medium and therefore increases the optical density and resolution. The spot size is diffraction limited.